Duplex metal sheet or article



y 2, 1956 F. E. DRUMMOND DUPLEX METAL SHEET OR ARTICLE Filed May 22,1953 FIG3 IN V EN TOR.

FOLSOM E. DRUMMOND Y loufirnuw ATT gala-JIM ORNEYS FIG-5 DUPLEX METALSHEET OR ARTICLE Folsom E. Drummond, Washington, D. C., assignor toCommonwealth Engineering Company of Ohio, Dayton, Ohio Application May22, 1953, Serial No. 356,697

4 Claims. (Cl. 29191.2)

This invention relates to duplex metal articles, and more particularlyis concerned with the production of a duplex metal sheet or the likecomprising a base of magnesium metal, or a magnesium alloy, having alayer of corrosion-resistant metal or metal alloy thereover which ishighly resistant to corrosion.

It has been proposed heretofore to produce magnesium alloy sheetscomprising a core of magnesium or magnesium alloy provided with acoating consisting of pure magnesium or a magnesium alloy which is moreresistant to corrosive attack than the core metal. Such duplex metals,however, have not been generally satisfactory because they possess thedisadvantage that at any point where the core or base metal is exposedin contact with the coating metal, as, for example, along a cut edge ofthe sheet, or where the coating has been perforated, an electrolytictype of corrosion is set up which causes a preferential attack on thebase metal resulting in an impairment of its structural properties.

This preferential or selective corrosive attack on the core metal willoccur when the core metal has an electrode potential greater than thatof the outer metal. Under these conditions a voltaic action may be setup between the two metals in contact with the corroding medium and theresultant electrolytic action tends to dissolve the core metal. Thistype of corrosive action seriously restricts the use of magnesium andcertain of the magnesium alloys as a core or base metal in thefabrication of duplex metal articles.

The preferred metal or alloy used is titanium, zirconium or alloysthereof wherein titanium or zirconium or both are the chiefconstituents. Other metals of group IV of the periodic table ofelements, e. g. hafnium, thorium, etc., may be substituted for all or apart of the titanium or zirconium, the high melting point metals ofgroup IVA being preferred. The A subgroup of group IV comprises theelements titanium, zirconium, hafnium and thorium.

It is an object of this invention to provide a duplex metal articleconsisting of a metal or alloy which corrodes readily (e. g. whensubjected to boiling glacial (99.5%) acetic acid, and which is protectedagainst this corrosive action by being provided with asheath coating orcovering of the metals or alloys of titanium, zirconium, hafnium andthorium.

Another object of the invention is to provide a duplex metal article inWhich the core or base metal is magnesium or magnesium alloy which isenclosed in a protective outer casing of a corrosion-resistant metal orsuitable alloy thereof, the same being preferably welded or gas-plated,or otherwise secured to the base metal so as to form a unitary laminatedmetal product.

Another object is to provide a corrosion-resistant duplex metal articlein which magnesium or various magnesium alloys may be used as the base,or core metal, and wherein the surfaces of the core metal are protectedby a sheath comprising said corrosion-resistant metal or metal alloy,and wherein there is provided a light-Weight metal article having thestructural properties of the combined metals or nited States Patent "icealloys. A magnesium sheet or article is thus provided having improvedcorrosion-resistant properties over magnesium metal or its alloys.

Briefly, the invention comprises a composite metal body, which may be inthe form of a sheet, tube or rod or the like wherein the base metal orcore comprises magnesium metal or a suitable alloy thereof and thesheath or covering layer of a corrosion-resistant metal as its principalconstituent. The sheath or covering layer may constitute from about 8%to 60% of the weight of the composite metal sheet, rod or bar, but formost purposes the preferred proportion is about 10 to 25% or less of theweight of the composite product.

One method of making a bonded composite sheet or rod is by coatingthesurface of the magnesium surface to be sheathed with molten metal, e.g.', spraying molten metal such as zinc, cadmium, oralloys thereof, andthen applying thereto a sheet or layer .of titanium or zirconium metal.The magnesium sheet and corrosion-resistant sheet being superimposed oneupon the other with the sprayed molten metal film at the interface, thesuperimposed sheets being heated to a temperature of about 600' to 700F. or above, but below the melting point of the interface bonding metal.The superimposed sheets while still hot are passed one or more timesbetween rolls adjusted to produce a substantial reduction in thethickness of the composite sheet. There results a magnesium base sheethaving a sheath of corrosion-resistant metal strongly bonded thereto.

Using crushed sponge titanium metal, which'is cheaper than titaniumalloy metals, a suitable bonding agent such as molten metal may beemployed to form the composite product. In this method crushed andscreened titanium sponge metal (300 mesh or finer) is distributed as apowdered layer over the cleaned surface of the magnesium or magnesiumalloy sheet and bonded therewith by the use of molten zinc, cadmium or asuitable alloy thereof, as described above. Where titanium alloyparticles are used which have a sufficiently low sintering temperature,the same may be united to the magnesium metal surface by sintering.Titanium metal in a pure state has a melting. point of around 1800 F.,so that the lower melting point of titanium is preferably used forsintering purposes. p

Zirconium metal, as produced by electrolysis of its double alkali metalfluoride salt, or by reduction of the oxide with calcium metal, may beused. Hafnium is used associated with zirconium from which, if desired,it.may be separated by fractional crystallization of the complexfluorides. Thorium metal may be prepared by the action of alkali metalon the halide, e. g. thorium chloride.

The corrosion-resistant metals are amphoteric and possess the common.characteristic of raising the electrode potential of the magnesium withwhich they are alloyed.

The reason why this particular group should exhibit this effect is notentirely clear, but probably has some relationship to theirrelativeposition in the periodic table. These metals raise the electrodepotential of the magnesium in varying degree, depending, first, upon theparticular metal or metals used and, second, upon the particular amountswhich may be added to the magnesium. The choice of the proper magnesiumalloy to be used as the coating material in combination with any givenmagnesium metal base depends upon a predetermined knowledge of theelectrode potential of the base metal in question.

The coating magnesium alloys containing one or more of the class ofmetals above described should have an electrode potential greater thanthat of the base metal. These different potentials are readily measuredin accordance with methods long known in the art against a standardelectrode. If the potential of the base metal is electronegative withrespect to the standard electrode, it "is not necessary that the coatingmetal be electro-positive with respectto the standard electrode, butonly that it be less electronegative than the base metal ,inorder to besatisfactory for the purpose of my invention. Therefore, throughout thisspecification and claims, where it is said thatfthe electrode potentialof the coating metal should be higher thanvthat of the base metal, it ismeant that the coating metalshould be more electropositive with respectto the standard electrode than is the base metal. While no fixedpotential difference is required between the electrode potential of thebase metal and that of the coating metal,- ;a substantial protectionmaybe given any base metal by. a coating metal of higher electrodepotential. Itis generally desirable that there be a relatively. Widediflerence in the electrode potential of'th e two metals,

since ;it has been found that with greater differences in potentialthere usually occurs less attackon the base metal, and by suitableadjustment of the potential difference'it ispossible to Iaiford the basemetal complete protection for all practical purposes. A convenientstandard electrode for measuring the potential. difference mentioned.may be readily selected from those now in regular use for similarmeasurements. .For the purpose of this description of the invention, acalomel electrode has been selected as a standard. 'In measuring theelectrode potential in question, the magnesium metal to be tested ismade one element ofan electrolytic cell; the calomel is made the otherelement. The electrolyte is a normal solution of sodium chloridecontaining 0.3 per cent by weight of hydrogen peroxide. The circuit isclosed and the potential difference of the elements is measured on apotentiometer. I

Titanium metal powder useful in practicing this inventionrnay beobtained from any suitable source and produced by different processes.One method of producing titanium metal is by the reduction oftitanium-tetrachloride with'magnesium. The resultant titanium metal isrecovered in the form of a spongy mass which is crushed to produce metalparticles of suitable size for incorporat 'ing into the coatingcomposition. 7

Although a titanium alloy of aluminum and chromiu is set out in anexample illustrating the invention, it' will be understood that otheralloys of titanium.may be employed. Titanium alloyed with up to 10% ofother Figure 3.

metals, e. g. molybdenum, tungsten, nickel, vanadium,

copper or iron, are illustrative of alloys which may also be used. a

The term corrosion-resistant metals, as used in the specification andclaims, is intended to include the metals and theiralloys of the IVgroup of the periodic table and mixtures of metal particles wherein themetals of this group constitute the major constituent.

The addition of one or more of the elements above described to thecorrosion-resistant metal for the purpose of forming the protectivecoating or alloy may be made and in any suitable amount necessary toattain'the desired electrode potential so long as other desirableproperties of the magnesium itself are notmaterially impaired; and,likewise, other elements not deleteriously affecting the deistics of themagnesium may be added. In general, the following amounts of the metalsof the class above described best serve the general purposes of thisinvention 'in producing the electrode potential desired withoutmateriallyimpairing other desirable properties of the magany magnesiummetalhaving the properties which it is desired to obtain in the finishedarticle." Yarious known alloys possessing known. combinations ofproperties may be used, such as a magnesium-base alloy comprising 6 tosired potential properties and other desirable character- 7% aluminum,and less than 1% zinc, the remainder being magnesium. Othermagnesium-base alloys commerically available which may be used besidesmagnesium are alloys containing tin (5% Zinc (4%) and manganese (1%),remainder magnesium. Also magnesium metal containing 1 to 3 manganese,with or without In the drawing:

Figure l is a perspectiveview of a duplex article or sheet. having acore 10 of magnesium metal and an outer covering or layer 1101? titaniummetal or alloy.

Figure 2 is a view in cross-section, illustrating a duplex metal articlein the form of a tube, and comprising a base metal 12 of iron, magnesiumor the like with an inner layer or liner 13'consisting of titanium metalor alloy containing chiefly titanium.

Figure 3 is a cross-sectional view of showing two sheets of metal 14 and15 being rolled and reduced in thickness while bonding the pair of metalsheets together, one of the sheets as at 14 being designated asmagnesium and reference character 15 representing titanium, zirconium orthe like metal.

Figure 4 illustrates in perspective and sectioned,'a solid rod having acore 16 of magnesium having an outer protectivelayer 17 of a suitablecorrosion-resistant metal.

Figure 5 is an enlarged cross-sectional view of a magnesium-base alloysheet 18 having a layer 19 of titanium, zirconium or the like metal,which may be applied by spraying the metal thereon.

As an alternative method of applying the corrosionresistant'metal overmagnesium metalsurfaces, the same may be deposited by gaseous metaldeposition. This may may be used. One method which has been foundparticularly useful is to roll together the coating alloy'and the basealloy in sheet or slab form as illustrated in It is satisfactory to castthe base alloy in an ingot mold lined with the coating alloy. Thearticle may then, if desired, be mechanically worked, as for example, byrolling or drawing or other suitable operation to form the particulartype of duplex article desired, such as sheet, rod or other form ofmaterial. The working with intermediate heating incident to such formingoperations tends to improve the bond between the coating metal and thebase metal. Duplex material may also be produced by spraying, gasplating or the like so as to provide the magnesium metal with anadherent coating of corrosion-resistant metal or alloy. This method maybe used to advantage where irregular shapes such as castings are to becoated."

The duplex articlesof the invention may be provided on any one or allexposed surfaces with the protective coating alloy,as for example areshown in Figures 1 and 2 of the drawing. Figure 1 shows a duplex articlecomprising a base 1 of a magnesium metal provided on its top and bottomsurfaces with a magnesium alloy coating. In Figure 2, a duplex metalarticle in tubular form comprising a base metal having an inner layer orcoating of titanium metal. This type of material is useful, for example,in the manufacture of pipes used to conduct a material to magnesiummetal.

What is claimed is: e

l. A corrosion resistant duplex metal article comprising a core ofmagnesium metal and a bonding layer thereover of a metal selected fromthe group consisting of zinc, cadmium and alloys thereof, and a layer ofmetal over said bonding layer of metal selected from the groupconsisting of titanium and zirconium.

2. A corrosion resistant duplex metal article comprising a core ofmagnesium metal and a bonding layer of zinc metal disposed thereover,and a layer of zirconium metal over said zinc metal.

3. A corrosion resistant duplex metal article comprising a core ofmagnesium metal and a bonding layer of zinc metal disposed thereover,and a layer of titanium metal over said zinc metal.

4. A corrosion resistant duplex metal article comprising a core ofmagnesium metal, a bonding layer of zinc thereover, and a layer of finetitanium metal particles sintered to said bonding layer of zinc.

References Cited in the file of this patent UNITED STATES PATENTS 6Brown Aug. 20, Stockmar Jan. 25, Alexander June 20, Bakarian Jan. 2,Diehl Jan. 2, Sears Dec. 13, DeLong Oct. 17, Scheer May 1, Maddex June12, Pessel July 17, Davis Nov. 25, Jordan Aug. 4, Pink Sept. 29, FinkJuly 6,

1. A CORROSION RESISTANT DUPLEX METAL ARTICLE COMPRISING A CORE OFMAGNESIUM METAL AND A BONDING LAYER THEREOVER OF A METAL SELECTED FROMTHE GROUP CONSISTING OF ZINC, CADMIUM AND ALLOYS THEREOF, AND A LAYER OFMETAL OVER SAID BONDING LAYER OF METAL SELECTED FROM THE GROUPCONSISTING OF TITANIUM AND ZIRCONIUM.